(1) Field of the Invention
This invention relates to a radiographic apparatus and a radiation detection signal processing method, based on radiation detection signals outputted from a radiation detector having numerous radiation detecting elements arranged in a two-dimensional matrix, for selectively acquiring desired images from among a plurality of radiographic images with the radiation detecting elements of the radiation detector assigned differently to the pixels of the radiographic images. More particularly, the invention relates to a technique for correcting abnormal radiation detection signals due to defects of the radiation detecting elements in the radiation detector.
(2) Description of the Related Art
A medical X-ray imaging apparatus (radiographic apparatus) includes a flat panel type two-dimensional radiation detector (hereinafter called “FPD” as appropriate) acting as a radiation detector for detecting transmitted X-ray images of a patient. As shown in FIG. 8, the FPD 2 has radiation detecting elements D arranged in a two-dimensional matrix of M rows and N columns, and thus M×N detecting elements D, on a radiation detecting surface to which the transmitted X-ray images of the patient are projected. Based on X-ray detection signals outputted from the FPD 2 as a result of X-ray emission to the patient to be radiographed, as shown in FIG. 9, an X-ray image P is created with m×n pixels Q arranged in a two-dimensional matrix of m rows and n columns, to be displayed on the screen of an image display monitor, for example.
On the one hand, the FPD 2, although lightweight and thin compared with an image intensifier, inevitably includes defective radiation detecting elements D resulting from a manufacturing process or the like. X-ray detection signals corresponding to the defective radiation detecting elements D are abnormal signals without proper pixel values (signal strength), and will produce defective pixels in the X-ray image P. Thus, the abnormal X-ray detection signals are corrected in real time by replacing the pixel values of each abnormal X-ray detection signal with the pixel values of surrounding normal X-ray detection signals, or with interpolation values calculated by using the pixel values of normal X-ray detection signals adjacent each abnormal signal. Such a technique is disclosed in Japanese Unexamined Patent Publication No. 2003-198937, for example.
On the other hand, a conventional X-ray imaging apparatus can provide, as X-ray images P, not only standard X-ray images but non-standard X-ray images different from he standard X-ray images.
The“standard X-ray image” refers to an image having pixels Q (i, j) arranged in the same two-dimensional matrix as the radiation detecting elements D, with the radiation detecting elements D (I, J) assigned in a one-to-one relationship to the pixels Q (i, j). For a standard X-ray image, M=m and N=n. The “non-standard X-ray image” refers to an image having pixels Q (i, j) to which the radiation detecting elements D (I, J) of the radiation detector are assigned differently from the standard X-ray image.
A non-standard X-ray image may, for example, be a foursome cluster X-ray image having four radiation detecting elements D in a 2×2 mini matrix arrangement of two rows and two columns assigned to each pixel Q (i, j). Another non-standard X-ray image may be an X-ray image of ¾ limited matrix having radiation detecting elements D in a center matrix range of (¾) M×(¾) N assigned to the respective pixels Q (i, j).
However, the conventional X-ray imaging apparatus noted above often fails to correct promptly the abnormal X-ray detection signals due to defects of the radiation detecting elements D.
When acquiring a standard X-ray image, abnormal X-ray detection signals to be corrected are known immediately and corrected promptly since the defects of radiation detecting elements D are stored in advance as defect information corresponding to the pixels Q in the standard X-ray image. However, for a non-standard X-ray image having pixels Q to which the radiation detecting elements D are assigned differently from the standard X-ray image, the defects of radiation detecting elements D are not stored in advance as defect information corresponding to the pixels Q. It is therefore necessary to collect output signals from the FPD 2 for defect information acquisition first, and then to check the presence or absence of defects in the radiation detecting elements D. As a result, when acquiring non-standard X-ray images, abnormal X-ray detection signals cannot be corrected promptly.